Conventionally, lithium ion secondary batteries and the like, for example, commonly use a structure wherein a battery container accommodating therein a power generating element is hermetically sealed. The battery container is provided with an opening because of the necessity to introduce liquid or the like into the container. This opening in a lid member will eventually be closed. One battery container for this type of sealed battery has a container body with an open end and a lid member closing that. In this case the above-mentioned opening for introducing liquid or the like is typically provided in the lid member.
Patent Document 1 is one example of the above. In the technique of Patent Document 1, a flat-shaped sealed battery is provided with a circular opening in a lid member for introducing liquid electrolyte. A sealing member is welded to this opening to close it after the liquid has been introduced. This welding is performed around the entire circumference of the sealing member. This is done in an attempt to provide a reliable hermetic seal for the opening.